Seed layer laser-induced deposition

ABSTRACT

A method of creating a layer of a target deposit-material, in a first target pattern, on a substrate surface. The substrate surface is placed in a vacuum and exposed to a first chemical vapor, having precursor molecules for a seed deposit-material, thereby forming a first substrate surface area that has adsorbed the precursor molecules. Then, a charged particle beam is applied to the first substrate surface area in a second target pattern, largely identical to the first target pattern thereby forming a seed layer in a third target pattern. The seed layer is exposed to a second chemical vapor, having target deposit-material precursor molecules, which are adsorbed onto the seed layer. Finally, a laser beam is applied to the seed layer and neighboring area, thereby forming a target deposit-material layer over and about the seed layer, where exposed to the laser beam.

This application is a Continuation of U.S. application Ser. No.13/600,735 filed Aug. 31, 2012, which is hereby incorporated byreference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of depositing material onto asubstrate.

BACKGROUND OF THE INVENTION

Charged particle beam induced deposition processes such as electron beaminduced deposition (EBID) or ion beam induced deposition (IBID) involvethe dissociation of surface-adsorbed precursor molecules via electron orion bombardment. As typically implemented, a gas-phase precursor isdelivered through a hollow needle positioned just millimeters from thesurface of a substrate located in a high vacuum system. Having formed anadsorbed layer on the substrate surface, the adsorbate-covered surfaceirradiated by a charged particle beam. As the charged particles crossthe substrate-vacuum interface, they transfer some of their energythrough inelastic scattering to the precursor molecules adhered to thesubstrate surface. If the energy transferred is sufficient, molecularbonds are broken and the precursor “dissociates” into stable, solidphase components and volatile by-products. The solid components attachto the surface forming a deposit, thus enabling the direct writing ofnanometer to micrometer sized features. This process is typicallyreferred to as deposition. The volatile by-products produced by thedissociation process, subsequently desorb from the substrate and areremoved by a pumping system.

It is well known that electron and ion beams can be focused to spotsizes smaller than those achievable with traditional light optics. As aresult, the features produced by charged particle beam induceddeposition processes can be made smaller than those produced by laserinduced processes such as pulsed laser deposition (PLD) and direct-writelaser-assisted deposition. However, because E/IBID are relatively slowprocesses, thick deposits or deposits made over large areas using thesetechniques can result in long processing times. In addition, the purityof the deposits made with charged particle beam techniques is often low.For deposits that are ideally conductive (e.g. platinum), low purity(e.g. carbon contamination) results in lower than ideal conductivity. Ingeneral, contaminant incorporation deteriorates the desired propertiesof the targeted material for deposition.

There are beam chemistry related references directed toward improvementof purity and/or material properties either through novel processing,post-processing, or novel precursor selection. One such referencedescribes a novel precursor, hexamethylditin, which can be used todeposit a high purity, low resistivity tin material with IBID. Anotheris a beam-seeded atomic layer deposition (ALD) technique work where anEBID seed is used to direct the growth via atomic layer depositions viacyclical spontaneous reactions. The result is a pure deposit localizedat the catalyst. Both techniques may have drawbacks, however. The tindeposition tends to work only in vias and subsurface features wherethere is a high degree of gas confinement. The ALD process can besomewhat slow and irreproducible and is subject to problems with vacuumcontamination. There are many references for continuous wave andnanosecond pulsed laser induced deposition with both photolytic andpyrolytic mechanisms. But these mechanisms tend to heat the substrate,which can be undesirable.

Accordingly, there is an unmet need for novel high purity depositionprocesses. In particular there is a need for processes that enable bothlarge and small area deposition of pure metals, dielectrics, andsemiconductors.

SUMMARY OF THE INVENTION

An object of the invention is to deposit a material in an arbitrarypattern onto a substrate.

In a first separate aspect, the present invention is a method ofcreating a layer of a target deposit-material on a substrate surface.The method begins with the placement of a substrate surface in a vacuumand the act of exposing the substrate surface to a first chemical vapor,comprised of precursor molecules which, when irradiated with a chargedparticle beam, form a deposited seed layer only in the region of chargedparticle irradiation. The purpose of the initialcharged-particle-induced localized deposition is that the depositedmaterial encourages subsequent deposition of the target deposit-materialby changing the optical absorption characteristics, changing thesticking coefficient/residence timeof the target deposit-materialprecursor gas, and/or lowering the activation barrier for dissociation.The result of the deposition of the seed layer is the formation of a newsolid surface that can subsequently be covered with a layer of precursormolecules. The seed layer is then exposed to a second chemical vapor(being the same or different from the original precursor) comprised oftarget deposit-material precursor molecules. The target deposit-materialprecursor molecules adsorb onto the seed layer. Finally, a laser beam isapplied to the substrate. A target deposit-material layer is formed overand about the intersection of the seed layer and the area to which thelaser beam is applied, which may be due to the aforementioned changes inactivation barrier, optical absorption properties and/or vaporadsorption properties. In one preferred embodiment the charged particlebeam is scanned over the substrate to form a patterned seed layer, butin another preferred embodiment it is held stationary.

In a second separate aspect, the present invention may take the form ofa method of depositing a layer of a target deposit-material onto asubstrate surface—having a seed layer that facilitates laser induceddeposition of the target deposit-material. The method begins with theplacement of the substrate surface area into a vacuum and the act ofexposing the substrate surface area to a chemical vapor comprised ofprecursor molecules for the target deposit-material. Then, a laser beamis applied to the area and a target deposit-material layer forms wherethe laser beam is applied to the seed layer.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more thorough understanding of the present invention, andadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic illustration of a first stage in the process ofthe present invention;

FIG. 2 shows a schematic illustration of a final stage of the process ofthe present invention;

FIG. 3 shows a plan view of a substrate region after performance of theprocess stage illustrated in FIG. 1;

FIG. 4 shows a plan view of the substrate region of FIG. 3 afterperformance of the process stage illustrated in FIG. 2; and

FIG. 5 is a flow chart of the process of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention are directed to method ofdepositing material on a substrate surface.

Definition: An ultrashort pulsed laser is a laser that emits pulses oflight with durations less than 10 picoseconds. Functionally, theultrashort regime is entered when the intensity dependence of thematerial response is dominated by the square (or higher order) of theelectric field. An ultrashort pulsed laser beam is a beam emitted by anultrashort pulsed laser.

Referring to FIGS. 1 and 5, a configuration 110, for implementing apreferred method 210 (FIG. 5) of practicing the present processinvention, includes, in a vacuum, a substrate 112 that is exposed to avapor 114 by a gas injection source 116 (step 212). Typically (but notnecessarily), source 116 is a needle positioned less than 1 mm over thesurface of substrate 112. Vapor 114 includes precursor molecules for aseed deposit-material, which become adsorbed onto the surface ofsubstrate 112, forming a layer of adsorbed molecules 115 (FIG. 3).

Irradiation of adsorbed precursor molecules 115 with a charged particlebeam 118 (step 214) results in the dissociation of the precursormolecules 115, and a deposit of a seed layer 120, of seeddeposit-material. In one preferred embodiment seed layer 120 is acatalytic metal, such as platinum. In this instance, the platinum layer120 is impure, apparently because the power density of a chargedparticle beam is insufficient to affect the complete dissociation of theprecursor molecules, so carbon and/or other atoms are deposited alongwith the platinum. A catalytic metal seed layer encourages deposition oftarget deposit-material by lowering the activation barrier fordissociation of the target deposit-material precursor molecules. Inanother preferred embodiment, the seed deposit-material changes thesticking coefficient/residence time of the target-deposit material orchanges the optical absorption characteristics of the substrate.

Following the creation of seed layer 120, the charged particle beam 118is discontinued and the seed layer 120 is exposed to a second vapor 122(step 216), which has precursor molecules of a target material, whichare also adsorbed onto the substrate surface, to form an adsorbed secondprecursor molecule area 124 (FIG. 4). The area 124 is contemporaneouslytreated with an ultrashort pulsed laser 126 (step 218). The result is ahighly pure deposit 128 of target deposit-material, closely matching,but slightly expanded from, the catalytic seed layer 120. In the casewhere deposit 128 is of platinum, it is of a much higher purity than thecatalytic seed layer 120.

Although in one preferred embodiment the target material is platinum,there are many other preferred embodiments, each depositing a differentmaterial on and about the seed layer. In an alternative preferredembodiment, the target deposit-material is carbon, and carbon precursormolecules are used to provide a carbon deposit 128, on seed layer 120.

In one preferred embodiment, the charged particle beam spot size on thetarget is on less than 10 nm. The catalytic see layer 120 is typicallywider that the spot size due to the spread of secondary and primarycharged particles. The line width of the catalytic seed layer 120 ispreferably between 100 and 150 nm, more preferably between 50 and 100nm, and most preferably between 10 and 50 nm. The line width of thelaser-induced deposit is preferably between 110 and 160 nm morepreferably between 60 and 110 nm, and most preferably between 15 and 60nm. The line width which compares favorably to the resultant widths fromcurrently available techniques and may be advantageously used in thecreation of micro-circuitry.

In another preferred method, a wider catalytic seed layer is created,which may have a closed geometric shape, such as a rectangle, eitherthrough the use of a wider charged particle beam 118, or throughscanning an area with the beam 118. Although other techniques are knownfor creating a pure layer of material, when there is no restriction asto width, the advantage of the present method is that a layer 120 ofpure target material can be created without subjecting the substrate, orthe layer 120 as it is being formed, to potentially destructive heat.The techniques described above may be performed at a wide range oftemperature, including about 20° C. (approximately room temperature).

As noted, in a preferred embodiment laser beam 124 is an ultrashortpulsed laser beam. This beam has the advantage of having a fluence thatis low enough so that no appreciable ablation or heating of thesubstrate occurs. In some situations, however, heating the substrate ispermissible. Accordingly, in alternative preferred embodiments, anothertype of laser is used, including picosecond, nanosecond, or continuouswave lasers.

In one preferred embodiment, vapor 114 includes molecules oftrimethyl(methylcyclopentadienyl) platinum, a platinum precursor. Inanother preferred embodiment, vapor 114 includes molecules of dicobaltoctacarbonyl, a cobalt precursor. A skilled person can readily determineother suitable precursor gases for the catalytic layer and for thedesired metal layer. Suitable precursors gases for the catalyst layer120 and the target material deposit layer 128 have the followingproperties: a high vapor pressure, deposit material-to-ligand bondenergy low enough to be disassociated by the charged particle beams butnot so low as to spontaneously disassociate, a high sticking coefficientand a long residence time. In one preferred embodiment substrate 112 isa semiconductor substrate, such as a silicon substrate, in anotherpreferred embodiment the substrate is an oxide, such as SiO₂. Ingeneral, a wide range of substrates may be used.

Deposition rates for the seed layer depend on the beam current, but atypical deposition rate is 0.4 um³/min. Laser-induced deposition of thetarget material (which may be pure metal) typically occurs at a rate ofbetween 0.8 and 1.2 um³/min, and more preferably between 1.0 and 1.5um³/min. The purity of the laser-induced deposition is typically greaterthan 40%, more preferably greater than 60%, and most preferably greaterthan 80%.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

In an additional preferred embodiment, the initial seed layer isdeposited, and the laser induced deposition process is performed asdescribed above. After this, however, an additional seed layer isdeposited, followed again by the laser deposition of a furthertarget-deposit material. This two-layer deposition process is performediteratively until a desired thickness is reached. This process can beused to cyclically create a layered deposit that adheres more closely toa desired shape and interior structure than would otherwise be possible.In one preferred embodiment, the precursor molecules for the furthertarget deposit-material layers are varied from one deposition cycle tothe next, to create an interleaved stack of materials. In thisembodiment, the precursor molecules for the charged particlebeam-deposited seed layers may also be varied, to optimize for multipletarget deposit-material layers. As an example, several differingprecursors could be used to create a stack of light emitting materialsand metals in-situ to allow for fabrication of a light emitting diode, adiode laser, a quantum well structure, or other light emitting device.

The following table lists precursor molecules that may be used in theprocesses described above. This is not a comprehensive list and isprovided by way of example.

TABLE LIST OF PRECURSOR MOLECULES Al(CH₃)₃ Trimethyl aluminum AlCl₃Aluminum trichloride AgBF₄ Silver tetrafluoroborate AuCl₃ Goldtrichloride AuCl(PF)₃ Gold chloride trifluorophosphine Au(CH₃)₂ (acac)Dimethyl gold acac Au(CH₃)₂ (hfac) Dimethyl gold hfac Au(CH₃)₂(tfac)Dimethyl gold tfac (C₄H₉)₄Au₂F₂ Tetrakis isobutyl diaurum difluoride(C₄H₉)₂AuF₂Pd(C₆H₁₁) Bis isobutyl aurum (III) cyclohexyl palladium(II)difluoride Co₂(CO)₈ Dicobalt octacarbonyl Co₄(CO)₁₂ Tetracobaltdodecacarbonyl Co(CO)₃NO Cobalt tricarbonyl nitrosyl Cr(C₆H₆)₂ Diarenechromium Cr(CO)₆ Chromium hexacarbonyl Cu-DMB-hfac Copper DMB hfacCu(hfac)₂ Copper di-(hfac) Cu-MHY-hfac Copper MHY hfac Abbreviations:acetylacetonate (acac), hexafluoroacetylacetonate (hfac),trifluoroacetylacetonate (tfac), dimethyl bipyridene (DMB),2-methyl-1-hexene-3-yne (MHY), vinyltrimethylsilane (VTMS), Cp(cyclopentadienyl)

We claim as follows:
 1. A method comprising; forming a layer of adsorbedseed precursor molecules on a surface of a substrate; irradiating thelayer of adsorbed seed precursor molecules with charged particles toform a seed layer; forming a layer of adsorbed target material precursormolecules on the seed layer; and irradiating the layer of adsorbedtarget material precursor molecules with a pulsed laser beam to form atarget deposit layer, wherein no heating of the substrate occurs whileirradiating the layer of adsorbed target material precursor moleculeswith the pulsed laser beam.
 2. The method of claim 1, wherein the pulsedlaser beam provides ultrashort pulses.
 3. The method of claim 1, whereinthe seed layer and the target deposit layer are formed from the samematerial.
 4. The method of claim 1, wherein the charged particles areelectrons.
 5. The method of claim 1, wherein the charged particles areions.
 6. The method of claim 1, further comprising: exposing the surfaceof the substrate to a first precursor gas, the first precursor gasincluding the seed precursor molecules; and exposing the surface of thesubstrate to a second precursor gas, the second precursor gas includingthe target material precursor molecules.
 7. The method of claim 6,wherein the first and second precursor gases are the same.
 8. The methodof claim 1, wherein the target deposit layer has greater purity than theseed layer.
 9. The method of claim 1, further comprising forming afilled closed geometrical shape of at least the target deposit layer.10. The method of claim 1, wherein the target deposit layer forms at arate of 0.8 μm3/min to 1.5 μm3/min.
 11. The method of claim 1, whereinforming a layer of adsorbed target material precursor molecules on theseed layer and irradiating the layer of adsorbed target materialprecursor molecules with a pulsed laser beam are contemporaneouslyperformed.
 12. The method of claim 1, wherein the target deposit layeris larger than the seed layer.
 13. The method of claim 1, furthercomprising: forming a second layer of adsorbed seed precursor moleculeson the target deposit layer; irradiating the second layer of seedprecursor molecules with charged particles to form a second seed layer;forming a second layer of adsorbed target material precursor moleculeson the second seed layer; and irradiating the second layer of adsorbedtarget material precursor molecules with the pulsed laser beam to form asecond target deposit layer.